The zeners will not conduct any noticable current until their threshold voltage is crossed. If you connect a few leds in series with resistance such that they will not exceed there maximum rated current below the maximum system voltage, then they will begin to glow once the voltage of the stepper exceeds the voltage drop across the diode or diodes for them to conduct. They would glow brighter as the voltage from the stepper increases. The zeners would then function as a shunt and allow lots of current to flow once the voltage increases past their rated value, the purpose being to prevent the system voltage from rising too far. You could have lots of fun with the design of the lighting. Leds begin to conduct at different voltages. This voltage is usually similar for similar colors, because the light given off by the led is of a particular frequency or energy, and the electrons flowing through the LED need to impart this energy to the photons.
Red LED's usually start to emit light when 1.2 volts or more is across their leads. Yellow Led's require slightly more voltage, Green LED's about 2.5 - 3 volts, blue and white LED's which are basically blue or ultraviolet leds with a phosphor begin to conduct a bright light from about 3 volts.
If you connect one red LED in series with a resistor, it will begin to glow at about 1.2 volts and will become brighter as the voltage increases. If the LED can handle 25 milliamps, and you size the resistor for a maximum voltage of 28 volts, then it would be (28 - 1.2)volts = .025 amps * (resistor value in ohms) which is equal to 1072 Ohms. The power turned into heat in the resistor in watts is equal to the current in amps multiplied by the voltage drop in volts. So it would be .025 Amps * (28-1.2)volts = .67 watts. Use a 1200 Ohm 1 Watt resistor for a bit of a safety margin.
If you connected two in series with a resistor, then it would begin to conduct when the some of the forward voltage drops across each diode is reached (1.2 + 1.2) = 3.4
The value of the resistor would then be (28 - 2.8)volts = .025 Amps * (resistor value in ohms) and solving for the resistor value we obtain 1024 ohms, so a 1200 ohm resistor at one watt would work here as well.
As you may already have guessed, if you connect more LED's in series, you will be turning a larger percentage of the energy into light in the LED's and a lower percentage of it into heat in the resistor.
You could make a star that gets bigger when the wind increases, or a simple bar graph that grows and changes color as the wind increases, or any of countless other effects.
The relay was a second idea for a control scheme, the relay coil could be hooked across a voltage divider circuit from the output of the alternator, or connected through an appropriate zener diode or several normal diodes to adjust the voltage the coil sees relative to the output of the alternator. That way the relay could be operated in a normally closed mode such that when the output voltage of the alternator exceeds a certain amount, the relay would open to protect the circuits attached from receiving too high of a voltage. You couldn't use this with a horizontal axis machine as once the electrical load was removed from the mill, the blades would speed up to point where the wind turbine might be torn apart from the forces, throwing a blade or two. With a vertical axis machine I do not think that that would be a problem.
Rich Hagen
